The present invention relates generally to a cordless blind, and more particularly to a cordless blind having a one way brake.
In a traditional venetian blind window covering, the slats are raised and lowered by a pair of lift cords. The lift cords are typically secured to a bottom rail and extend upward through the slats into a head rail. The lift cords are guided within the head rail and exit through a cord lock. The lift cords hang outside of the window covering, may present a safety concern to small children and pets. In order to raise or lower the window covering the lift cords must be manipulated to first release the cord lock. Similarly, once the window covering has been raised or lowered the cord lock must be manipulated again to lock the cords in place.
Blinds and shades in which the lift cords are contained within the bottom rail, window covering and head rail are referred to as cordless blinds and shades, since no portion of the lift cords are external to the blind or shade. Cordless blinds have been gaining popularity and are employed in a wide variety of blinds and shades such as Venetian blinds, cellular blinds, pleated shades, and wood blinds.
One type of cordless blind disclosed in U.S. Pat. Nos. 5,482,100; 5,531,257; and 6,079,471, and incorporated herein, utilizes a spring motor to apply a spring force to the lift cords to bias the bottom rail and accumulated window covering toward the top rail. In a balanced window blind system, the spring force of the spring motor, system frictional forces and the combined weight of the bottom rail and accumulated window covering are selected to balance the bottom rail relative to the top tail. In such systems the frictional force is greater than the difference between the spring force and the combined weight of the bottom rail and accumulated window covering when the bottom rail is at any location between a fully extended position and a fully retracted position.
If the system is not in balance as described above, the bottom bar will either move upward or downward depending on the imbalance in the system. For example if the spring force is greater than the weight of the bottom bar and accumulated window covering and the frictional forces in the system, then the bottom bar will continue to be biased upward toward the head rail, until the weight of the accumulated window covering balances the system. Similarly, if the spring force and frictional system forces are less than the weight of the bottom bar and accumulated window covering the bottom bar will move downward away from the head rail.
Since the weight of the accumulated window covering increases as the bottom bar moves toward the head rail, it is possible that the spring force causes the bottom bar to move toward the head rail when the bottom rail is fully extended, but when the bottom rail is close to the head rail, the weight of the bottom rail and accumulated window covering causes the bottom bar to move away from the head rail.
One type of cordless blind that employs a spring to bias the lift cords is described in U.S. Pat. No. 6,029,154 in which a brake is applied to the spring motor to prohibit the bottom member from moving toward or away from the head rail without the brake being released. Similarly, U.S. Pat. No. 6,029,734 discloses a bind having a spring motor in which a brake is applied directly to the lift cords within the bottom rail to prohibit the bottom member from moving toward or away from the head rail. This brake system allows the use of a cordless blind without the need to ensure that all of the forces are in balance. Since, neither of the blinds are balanced, the brake mechanisms disclosed in the ""154 and ""734 patents prevent the lift cords from either unwinding or retracting thereby preventing the bottom rail from moving either toward or away from the head rail until the brake is released.
There are a number of problems with this type of brake system. First, an operator must release a brake mechanism before raising or lowering the blind. Additionally, if an operator fails to release the brake mechanism before pulling the bottom bar downward, the brake mechanism may be damaged or the blind itself may be damaged.
Further, if the blind is raised to the full open position such that bottom rail is close to the top rail, it may be difficult for a user to disengage the lock at that height.
Accordingly, it would be desirable to provide a cordless blind having a brake mechanism that would permit the blind to be lowered without requiring the brake to be released. It would also be advantageous to provide a cordless blind having a brake mechanism in which the bind could be raised by manual biasing of the bottom rail toward the top rail without releasing the brake.
A window blind comprises a head rail, a bottom rail and a window covering extending between and operatively connected to the head rail and bottom rail. At least one lift cord extends between the bottom rail and the head rail. A spring motor operatively coupled to the lift cord biases the bottom rail toward the head rail. A one way brake prohibits the bottom rail from moving toward the head rail but permits the bottom rail to be moved away from the head rail by an operator.
In another embodiment a window blind comprises a head rail, a bottom rail, and a window covering extending between and operatively connected to the head rail and bottom rail. At least one lift cord extends between the bottom rail and the head rail. A spring motor is operatively coupled to the lift cord to apply an upward force on bottom rail toward the head rail. A one way brake in an engaged position prohibits the spring motor from moving the bottom rail in a first direction relative to the head rail and permits the bottom rail to be moved in a direction opposite to the first direction relative to the head rail. A switch is located in the bottom rail and is operatively connected to the one way brake to disengage the one way brake to permit movement of the bottom rail in the first direction.
In a further embodiment a window blind comprises a head rail and a bottom rail. A window covering extends between and is operatively connected to the head rail and bottom rail. At least one lift cord extends between the bottom rail and the head rail. A spring motor is operatively coupled to the lift cord to apply an upward force to the bottom rail toward the head rail. A one way brake prohibits the bottom rail from moving away from the head rail but permits the bottom rail to be moved toward the head rail by an operator.